If you sign a trust deed then you are agreeing that you will pay across whatever is reasonably affordable each month, as agreed with your trustee. Having said that, a little can usually be set aside to save up for emergencies and I would encourage anyone to try and do so.

In answer to your second question, your creditors can apply to make you bankrupt if they choose to, as can your trustee, though this is not usually what happens. Most people apply for bankruptcy themselves as their next preferred option, though you do not have to do this if you feel strongly that you would rather not. If not then you would still be in a trust deed, albeit not protected.

The vast majority of trust deeds do become protected, however, and even if you did get objections, these may be able to be overcome by a spot of negotiation (eg offering to pay over a longer term).